1-We don't know if they left the building or not, but if they had been told to leave the building they would have left it.
I was taught that the third type conditional was always counter-factual, but could it work in cases when one does not know what the facts were?
In the above sentence, the speaker does not know whether they left the building or not, nor whether they were told to or not. He is merely stating that if they were told to leave the building, they had to leave it. Is the sentence acceptable in such a context?